Mr Clegg explained: "There were a number of reasons for that; one obviously was newspapers are very competitive with each other, and some journalists may be anxious to try to steal a scoop from a rival.

"One of the reasons for the sweeps was to avoid that possibility.

"In 2011, News Corp was trying to increase its shareholding in BSkyB, I think with the objective of becoming the majority shareholder.

"It was a sensitive topic at News Corp, and another reason why you would want to be sure discussions about such a matter were not broadcast to people who were potential competitors."

The court heard executives from News Corp Europe and Asia had offices in Wapping, and were part of the sweeps carried out by Mr Hanna, through a contracted company called White Rock.

In an email sent by Brooks to fellow executive Will Lewis and Mr Hanna on January 25, 2011, she wrote: "Can we have my phones, email, office swept...thanks, discreetly."

Jane Viner said that request was "a perfectly routine request from an executive."

Mr Hanna, who served in the first Gulf War, was also charged with advising journalists about personal safety if they were planning to report from a war zone.

He was also in charge of dealing with a slew of hate mail being sent to the offices in Thomas More Square when the phone hacking scandal broke.

"Threatening mail had in fact been received at Thomas More Square addressed to some in the executive," said Mr Clegg.

"There was a perceived heightened risk at Thomas More Square, and a perceived heightened security risk to News Corp executives.

"Mark Hanna was instructed to organise protection for these various executives perceived to be at risk."

Mr Clegg said the security risk had "never been higher" in July 2011, when protection plans were in place for Brooks, Mr Lewis, and another executive, Simon Greenberg.

Brooks was codenamed Blackhawk, while the other two were given the security names Kestrel and Sparrowhawk by security teams protecting them.